If you want 6x9 and want to change lenses, you're basically limited to something like a Mamiya Press camera.
Not the sharpest lenses, but great camera system for hand-held. I guess perhaps that, it being a press camera, Mamiya didn't see the need to including fantastic optics.
I have a relatively complete Mamaya Universal Press system, includ9ng multiple lenses. For example, it makes a nice vacation system. It was designed as handheld, so being able to take snapshot type photos is its forte.
At the same time, one can mount it on a tripod, use an accessory ground glass for composing and focusing, and engage in fine art photography. One nice thing, the Mamiya press system has interchangeable backs, so switching films is easy. Mamiya backs are known to hold film very flat. They also come in different formats, 6x6, 6x7, 6x9. With the G accessory back, the Mamiya Universal can accept Graflex, medium format backs, or even Mamiya RB67 backs. (It will not accept Horseman, nor Wista backs.)
Actually, it's possible to get two standout lenses with this system. A bit expensive, the 100mm f2.8 is supposed to be very sharp. As a Biogon design, the same can be said of the 50mm Mamiya Press lens that covers 6x9.